add module example

Author: hallazzang

examples/syscall/module/main.go

@@ -0,0 +1,18 @@
+package main
+
+import (
+	"golang.org/x/sys/windows"
+)
+
+func main() {
+	caption, err := windows.UTF16PtrFromString("Go Windows Programming")
+	if err != nil {
+		panic(err)
+	}
+	text, err := windows.UTF16PtrFromString("Calling MessageBox from Go!")
+	if err != nil {
+		panic(err)
+	}
+
+	messageBox(0, text, caption, 0)
+}

examples/syscall/module/syscall.go

@@ -0,0 +1,24 @@
+package main
+
+import (
+	"unsafe"
+
+	"golang.org/x/sys/windows"
+)
+
+var (
+	libuser32 *windows.LazyDLL
+
+	procMessageBoxW *windows.LazyProc
+)
+
+func init() {
+	libuser32 = windows.NewLazySystemDLL("user32.dll")
+
+	procMessageBoxW = libuser32.NewProc("MessageBoxW")
+}
+
+func messageBox(hWnd uintptr, lpText *uint16, lpCaption *uint16, uType uint32) int32 {
+	r1, _, _ := procMessageBoxW.Call(uintptr(hWnd), uintptr(unsafe.Pointer(lpText)), uintptr(unsafe.Pointer(lpCaption)), uintptr(uType))
+	return int32(r1)
+}